Various types of depression have been treated for years with so-called serotonin reuptake inhibitors. These active ingredients, also known as SRIs, are said to act as antidepressants in the brain and block – or at least reduce – the excessive transport of the neurotransmitter serotonin. Its level is considered disturbed by those affected. Because a higher concentration of serotonin can brighten the mood, so the idea – or vice versa: too little serotonin causes depression.
We know that we know nothing
However, the serotonin thesis has never been conclusively chemically proven. All that is known is that SSRIs seem to work in depressed people – and they are regularly given in conjunction with psychotherapy. A study published in Molecular Psychiatry this summer argues that we obviously know far less than previously assumed – and that low levels of serotonin in the brain do not necessarily trigger depression. The umbrella review – covering both meta and systemic analysis – by the group at University College London (UCL) even comes to the conclusion that there is “no evidence” for the serotonin thesis.
It’s “always hard to prove a negative,” said lead author Joanna Moncrieff, a professor of psychiatry. “However, after looking at the numerous research results over the last few decades, we believe we can say with certainty that there is no convincing evidence that depression is triggered by abnormalities in the area of serotonin.” Many people are prescribed antidepressants because they are told that depression is a biochemical trigger. However, according to Moncrieff, there was actually no evidence for this. It has still not been proven that there are differences in the serotonin level of healthy and depressed people when measuring the metabolites in blood or brain fluid.
A look into a misunderstood brain
According to Moncrieff & Co., research on the receptors responsible for the neurotransmitter and on the proteins responsible for serotonin transport has so far only found “weak and inconsistent” evidence that there are special serotonin activities in depressed people comes. Even worse: If such connections are discovered, they could in turn be due to the administration of antidepressants themselves.
Then there are studies that have attempted to reduce serotonin levels in healthy people by removing from their diet the amino acid necessary for serotonin production. A review of these studies by Moncrieff and her team found that depressive disorders did not occur “in hundreds of subjects.” There is only a very weak association in a subgroup of people who have a higher family history of depression. The study had 75 participants, but recent research is inconclusive.